Forest Investment Account (FIA) - Forest Science Program
FIA Project Y092116

    Growth of 10 tree species in relation to location and microclimatic gradients in a strip shelterwood
Project lead: Comeau, Phil (University of Alberta)
Contributing Authors: Hossain, Kazi L.; Comeau, Phillip G.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Shelterwood systems are applied in southern British Columbia to facilitate forest regeneration and to achieve visual and watershed management objectives. Although designed to regenerate even-aged stands, they provide opportunities to establish regeneration and achieve greenup of initially harvested areas, before the final removal cut. Group and patch shelterwood systems may be desired to maintain or recreate naturally patchy forests and can be easier to harvest and can be more amenable for creating conditions that favour regeneration of moderately tolerant to intolerant tree species than uniform shelterwood systems. Group shelterwood systems can also be less susceptible to windthrow.

Due to patterns in light, air temperature, soil temperature, and soil moisture, establishment and growth of regeneration is influenced by both the size of the openings and proximity to the edge of the uncut stand (Coates 2000; Huggard and Vyse 2002). Light levels increase as opening size increases and south sides of openings are typically influenced by shade from adjacent stands, resulting in lower amounts of direct sunlight near the southern edge compared to the northern edge (Messier 1996; Coates 2000; Delong et al. 2000; Spittlehouse et al. 2004). Light levels also generally increase under the intact stand located to the north of newly created openings. Snow may persist longer in the spring near the south edges of gaps compared to north edges (Huggard and Vyse 2002; Spittlehouse et al. 2004). Air and soil temperatures tend to increase with opening size and are higher at the north edge, adjacent to the edge of the stand, than at the south edge due to higher energy inputs associated with higher levels of direct sunlight (Huggard and Vyse 2002; Grey et al. 2002; Spittlehouse et al. 2004). Air and soil temperatures may also increase for a short distance under the intact stand to the north of large openings. Numerous studies indicate reductions in soil moisture, compared to that at the center of large openings, that extend up to 1 tree length into openings from the adjacent stand (Coates 2000; Gray et al. 2002; Spittlehouse et al. 2004). Few studies have documented effects of openings on nutrient availability in western forests. However, Huggard and Vyse (2002) report a significant increase in soil nitrate and a decrease in soil potassium in openings, compared to under the adjacent forest, and a rapid change between the forest and gap condition.

Seasonal patterns in resource availability can influence growth patterns and tree morphology. Year to year variations in these seasonal patterns can also result in differences in growth responses and in morphological features such as height:diameter ratio. Some studies suggest that an understanding of seasonal patterns of resource availability may be useful in understanding the effects of competition and other limiting factors on tree growth (Kimberley and Richardson 2004). Due to the multiple environmental factors influencing growth in small openings, an understanding of the seasonal dynamics and interacting effects of major environmental factors on physiology and growth of trees may lead to a better understanding of the effects of these factors. Understanding limiting factors to tree survival and growth and the effects of silvicultural practices on these limiting factors is widely recognized as a key to successful silviculture prescriptions.

Light, air temperature, soil temperature and soil moisture gradients across openings and differences in requirements and tolerances of tree species result in variation in which species grow well in and dominate particular environments. Studies in other parts of B.C. show clear patterns of tree growth in relation to light levels, and size and location in gaps which generally reflect the shade tolerance of the species. At Date Creek, near Smithers, Coates (2000) reports that the five species examined (western redcedar, western hemlock, subalpine fir, hybrid spruce and lodgepole pine) all showed asymptotic increases in rates of height and diameter growth with increasing gap size. While at largest gap sizes, tree size at age 5 generally declined with increasing shade tolerance, these differences were small in medium and small gaps. Initial results from Burton Creek suggest highly variable height growth responses, with shade tolerant western hemlock performing significantly better than less tolerant Ponderosa Pine and Douglas-fir (Delong et al. 2000). At Date Creek, the advantage of increased light at the north edge of large gaps appears to have been negated by competition for water for extending 10 m into the gap from the dripline of the surrounding stand (Coates 2000). A similar effect has been observed at Burton Creek. In a Sierran mixed conifer forest in California, tree growth responses varied in response to light and soil moisture availability, with between species differences occurring as a result of their requirements and tolerances to light and soil moisture (York et al. 2003).

A study (EP1191) examining the growth of ten tree species planted across clearcut strips was initiated at Burton Creek in 1994 (DeLong et al. 2000). Two small (50 m wide by 150 m long) clearcuts were created in a mixed stand dominated by Douglas-fir, western redcedar, and western larch. The long axis of each clearcut goes east-west. Seedlings of each of ten species (Douglas-fir, western larch, Engelmann spruce, western redcedar, western hemlock, white pine, ponderosa pine, lodgepole pine, subalpine fir, and paper birch) were planted at 3 m spacing in rows oriented north-south across each block in the spring of 1995 extending 20 m into the uncut stand south and north of each clearcut. Three replicate rows were established for each species. Various data were collected at this site through 1999, with limited analysis and reporting. Maintenance of all planted trees in this experiment is underway under LTRI055 by Michaela Waterhouse.

The purpose of the proposed study is to collect additional tree growth and microclimate data at Burton Creek during 2007, 2008 and 2009, analyze these data and available data from previous years, and summarize the results in published reports that will include development of a “gap environment” classification for similar Interior Cedar Hemlock zone stands. Results will also be presented during field tours and as SISCO and other workshops and conferences. This data can be linked to other silvicultural system trials within the southern interior (EP1186 proposal #Y081145). It will provide more detailed data on edge effect and species performance in partial cutting situations.

Work during 2008 will involve some minor modifications to work originally planned. Major changes involve making photosynthesis measurements at 21 day intervals for 4 species (Douglas-fir, interior spruce, western redcedar, and western hemlock) instead of 10 - since time and budget make it impossible to measure 10 species, and since several other species are not well represented in all gap environments. Additional sensors (6 rows of sensors with one sensor placed at the center of each of the 12 gap environments along each row) will also be installed to provide better sampling of soil moisture and temperature patterns across the two blocks.
Related projects:  FSP_Y081116FSP_Y103116


Executive summary (20Kb)
Extension Note (49Kb)
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Updated August 16, 2010 

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